Foreign objects such as wear dust produced from gears exist in transmissions mounted on vehicles such as automobiles and construction machinery. Rolling bearings used in such transmissions therefore include seal members which prevent entry of foreign objects into the bearing interior space, thereby preventing premature breakage of the rolling bearings.
Such seal members usually include a seal lip made from e.g., rubber. Bearing parts that rotate in the circumferential direction relative to the seal members, such as bearing races or slingers, are formed with seal sliding surfaces with which the seal lips of the seal members are in sliding contact. In this arrangement, since the seal lips are in sliding contact with the respective seal sliding surfaces over the entire circumference thereof, the drag resistance of the seal lips (seal torque) is high, which results in increased bearing torque. Also, the friction due to such slide contact increases the temperature of the rolling bearing. The higher the temperature of the bearing, the more strongly the seal lips tend be pressed against the seal sliding surfaces due to an increased pressure difference between the interior space of the bearing and the exterior of the bearing, thus further increasing the friction therebetween.
In order to reduce the seal torque of such a seal member, which is in contact with the seal sliding surface, JP Patent Publication 2007-107588 A proposes to subject the seal sliding surface to shot peening to form minute undulations thereon such that the seal sliding surface has a maximum roughness Ry of 2.5 micrometers or less, thereby promoting the formation of oil film between the seal lip and the seal sliding surfaces by lubricating oil trapped in the recesses of the minute undulations.